Method of casting



July 7, 1925. 1,544,930

C. PACK METHOD OF CASTING Filed Dec. 1, 1922 f INVEN TOR.

A TTORNEYS Patented July 7, 1925.

UNITED STATES 1,544,930 PATENT OFFICE.

CHARLES PACK, OF ELMHUR ST, NEW YORK, ASSIGNOR TO DOEHLER DIE-CASTING COMPANY. A CORPORATION OF NEW YORK.

METHOD OF CASTING.

Application filed December 1, 1922. Serial No. 604,124.

To all whom it may concern:

Be it known that I, CHARLES PACK, a citizen of the United States, residing at Elmhurst, in the county of Queens and State 6 of New York, have invented certain new and useful Improvements in Methods of Casting, of whichthe foilowing is a full, clear, and exact description.

My invention relates to the art of casting 10 and has especial reference to the making of metallic castings having an internal undercut. The removing of thecore from such castings is a problem the solution of which depends upon the size and shape of the cavity and also upon its surface design.

\Vhere a collapsible core cannotbe used to advantage, recourse is had to a fusible core,

i. e., one whose melting point is sufficiently lower than that of the casting to allow the core to be melted out, orto a core composed of a metal irrespective of its melting point, which is softer than that of the casting so that the core may be forcibly pulled out, the metal behind the undercut being sheared or gouged or displaced as the-core is withdrawn, or so that it may be bored and the remaining shell sprung or distorted to get it out. This the art of die-casting. In my prior Patent No. 1,416,412 patented May 16, 1922,- I have explained a method for using fusible cores, such as the casting of aluminum alloys upon lead or zinc or their alloys for the core, and in my co-pending application Serial Num- 88 her 604,122 and in my Patents Numbers 1,491,816 and 1,491,817, I have explained other methods of casting undercuts and removing the cores. The latter methods are articularly a plicable to cases where there 4 1s a delicate I esign to be reproduced, and I propose in those applications, by way of example, to form the core of aluminum and cast an aluminum-copper alloy upon it. While the fusing point of the aluminum is above that of the alloy, it is desirable to raise the temperature of the molten metal as high as practicable to obtain perfect fluidity, even higher than the fusing point of the core.

It has heretofore been considered impractical to cast a metal directly upon a metallic core, the fusing point of which is substantially below the temperature at which the metal is poured, and, to prevent the fusin of the core and casting together in such problem is frequently met in 7 cases, it has been the practice to provide the core with a coating of material having a higher fusing point, as described in my said prior Patent No. 1,416,412.

I have found that by taking into consideration such factors as the specific heat and melting points of the core metals and of the casting metals or alloys and controlling the temperature of the molten metal to regulate the amount of heat that is transferred to the core, I can cast directly upon the bare core even though the temperature of the molten metal be above the melting point of the core metal. In die-casting the casting is poured in such a minute period I of time and the casting metal cools and sets so quickly, that with a great variety of casting and core metal combinations it is possible to cast upon a core the fusing point of which is considerably below the temperature of the casting.

For instance with die-castings of the average mass I have found it entirely practical to castan aluminum-copper alloy having a melting point of substantially 1080" F. to 1300 F. or even higher, upon a pure aluminum core the melting point of which is substantially 1250 F. The reason for this is that the specific heat of aluminum is such that there is not enough heat transferred to the core to fuse its surface and cause it to stick at any point to the casting] The conductivity of the aluminum to heat is so good that the heat transferred to the core is uick- I conducted away and evenly distri uted throughout the mass of the core. In employing this combination of metals, therefore, I am careful to keep the tem erature of the molten alloy at not materially higher than 1300 F. The character of the aluminum core is such that it can be removed either by directly pulling it out, thereby shearing or gouging the metal against the harder overhanging wall of the casting or by reducing it to a shell and springing or distorting the shell to get it out.

With like precautions die-casting metal may be cast about a core of lower fusing point. I am able to cast aluminum. or alumlIlllXIl alloy about a bare zinc or zinc alloy core, and afterwards melt out'or otherwise remove the core. Similarly zinc or zinc alloy can be cast about a coreof bare lead or lead alloy, and lead or lead alloy can be cast about a core of tin or tin alloy,

With the aid of the accompanying drawings 1 shall now explain one application of my invention and shall thereafter point out my invention in claims.

Fig. 1 is a central section of an assembled die with a core and casting therein, the core being shaped to form an undercut such as to call for the application of my invention.

Fig. 2 is a central section of the die on a plane at right angles to that of Figure 1.

Fig. 3 is a plan of the core and casting, and

Fig. 4 is a side elevation of the casting after the core is removed.

It will be understood that the particular shape or design of the casting is immaterial, but by way of illustration I have shown a casting 1 which is a hollow frustum of a cone open at the top and closed at the b0ttom. The core 2, whicn is correspondingly s aped, has a stem I3 which is anchored in the recess 4 of the half die The other half die 6, which contains the mold cavity 7, is in two parts, dividing at the middle plane 6 as shown to enable the removal of the undercut casting. The sprue opening or gate 8 is at the center of the outer face of the half die 6 leading to the center of the base of the mold cavity, and consequently is disposed half on one side and half on the other side of the parting line (3.

Since the cored or interior surface of the casting is plain. the core 2 may he: fusible, i. e., it may lie of a mcial whose fusing point is suliicicntly below that of the casting to allow it to he melted out. For example, the casting metal may he an almuinum-copper alloy with a melting point of substantially 1080 l. and the core may be of zinc or a zinc alloy with a melting point of substantially 780 F. The reiative mass of the casting and core is such that, with the casting metal at the proper temperature to pour readily, there will not be sufiicient heat transferred to the core to cause surface fusion. After the casting is set, heat is applied slowly to the casting with the core therein for a suflicient length of time to raise the core to about 780 F. and melt it out.

It is obvious that my invention is in no wise confined to the particular details of the steps as explained above, but that the details may be variously modified by those skilled in the art to adapt the method to particular conditions without departing from the spirit and scope of my invention as pointed out in the appended claims.

I claim:

1. The method of making castings with an internal undercut consisting in casting directly upon a suitably shaped metal core, a metal at a temperature which is above the fusing point of the core but below that which will supply sufficient heat to the core to raise its surface to the fusing point.

2. The method of making castings with an internal undercut consisting in casting directly upon a suitably shaped lnetal core, a metal at a temperature which is above the fusing point of the core but below that which will supply sufficient heat to the core to raise its surface to the fusing point, allowing the casting to set, and then removing the core.

3. The method of making castings with an internal undercut consisting in casting directly upon a suitably shaped metal core, a metal having a higher fusing point than the core and at such a temperature that the heat transference during the casting operation will he insuliicient to raise the core surface to the fusing point, allowing the casting to set, and then melting out the core from the casting.

In Witness whereof. I hereunto subscribe my signature.

CHARLES PACK. 

